Synthetic Routes (Cambridge International A-Level Chemistry)

Analysis of Synthetic Routes

Worked Example The synthesis of compound X takes place in 2 steps:

OHCCH2CHO	$\overset{\mathrm{step}1}{\rightarrow}$	intermediate	$\overset{\mathrm{step}2}{\rightarrow}$	HO2CCH(OH)CH2CH(OH)CO2H
				compound X

Which reagents could be used for this synthesis?

Answer:

• The first step involves a nucleophilic addition of CN^- using NaCN as catalyst and heat to form a hydroxynitrile
• In the second step, the nitrile is refluxed with dilute aqueous sulfuric acid causing hydrolysis of the nitrile forming a carboxylic acid and ammonium salt

Worked Example The synthesis of hexanoic acid takes place in 2 steps

1-chloropentane	$\overset{\mathrm{reagent}X}{\rightarrow}$	compound Z	$\overset{\mathrm{reagent}Y}{\rightarrow}$	hexanoic acid

Which reagents could be used for this synthesis?

Answer:

• Halogenoalkanes can undergo nucleophilic substitution with ethanolic KCN in which the CN^- ion acts as a nucleophile and replaces the chlorine atom in 1-chloropentane to form a nitrile.
• The treatment of nitriles with concentrated hydrochloric acid will produce a carboxylic acid and an ammonium salt.
• In this case, hexanoic acid and ammonium chloride will be formed.